Rendering cellulosic materials non-adherent



United States Patent 9 3,004,871 RENDERING CELLULOSIC MATERIALS NON-ADHERENT Herbert Jack Leavitt, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York No Drawing. Filed July 23, 1959, Ser. No. 828,949 7 Claims. (Cl. 117-143) This invention is concerned with rendering cellulosic materials non-adherent to various organic materials. More particularly, the invention is concerned with the process for rendering paper or paperboard non-adherent to normally adherent materials such as, for instance, asphalts, bitumen, tars, waxes, paraflin solids, flour-containing pastes and frozen food stuffs, and other high molecular weight polymers and adhesives, which process comprises treating said cellulosic material with a mixture of ingredients comprising (1) a linear polydimethylsiloxane, (2) a polyalkyl silicate, (3) a methyl hydrogen polysiloxane, and (4) a metallic salt selected from the class consisting of dibutyl tin dilaurate and dibutyl tin diacetate.

Cellulosic fibers in the form of cellulosic papers and paperboard are used extensively as confining and shipping means for vairous highly adhesive materials including such organic compositions as asphalt or pitch, tar, various unvulcanized rubbers, particularly synthetic rubbers, other high molecular weight organic polymers used as adhesives, etc. For optimum use of these cellulosic containers, it is essential that they be capable of being readily separated or stripped from the cargo contained therein. Thus, in the transportation and shipment of asphalt used for roofing purposes, the asphalt is generally poured while still hot into a container, such as a carton, bag or drum whose sides are cellulosic in nature. After cooling, the asphalt becomes quite hard and can be readily transported with little difliculty. At its destination of use, it is essential that this paper in whatever form be capable of being readily stripped from the asphalt so as to permit easy access to the latter without any extraneous portions of the paper or fibers thereof adhering to the asphalt so as to undesirably afiect the constitution of the asphalt.

Various treatments have been accorded these types of papers which are often referred to as anti-blocking paper (or release paper). One method for treating the paper to render it anti-blocking comprises treating the paper in a three-coat operation with (l) finely divided clay and casein, (2) finely divided clay, and (3) polyvinyl acetate. Such paper provides release by fracture of the clay coating, but the polyvinyl acetate remains on the adhesive material. Another method commonly employed in the art involves applying several thicknesses of polyethylene to the paper, usually by treating the latter with solutions of the polyethylene. A still further method for treating cellulosic material to render it non-adherent, particularly to asphalt and to permit it to be readily removed from direct contact with the latter, involves depositing a double coating of cellulosic materials, the first coating being of clay and the second coating being of methyl cellulose and starch.

However, all the foregoing methods have been exceed ingly expensive and in many respects have not been too satisfactory since too often it has been found that these adhesive materials, particularly asphalt, which apparently has a high atfinity for cellulosic fibers, stick to the antiblocking paper so that great difiiculty is encountered in attempting to separate the latter from the asphalt.

US. Patent 2,588,367 describes the use of methyl hydrogen polysiloxanes in combination with water-soluble cellulose ethers for the purpose of treating anti-blocking paper to render it less adherent to ordinarily adhesive 3,004,871 Patented Oct. 17, 1961 "ice organic compositions. Although such combination of ingredients are ordinarily helpful in reducing the adhesive properties of the paper, nevertheless much is left to be desired from such treatment of the paper. Often, the release properties are unreliable and the release characteristics are not uniform throughout the surface of the paper. In addition, it is essential that, in order to obtain optimum release properties, the treated paper be aged for extended periods of time, e.g., by storage before it is useful for release purposes; this is necessary because accelerated aging by high temperature treatment is not usually available commercially in paper-treating establishments. Furthermore, paper such as parchment paper cannot be heated above C. without deleteriously affecting the paper. Moreover, after treatment of paper with the combination of methyl hydrogen polysiloxane and cellulose ether, the abhesive characteristics (i.e., the release properties) tend to decrease with time so that after long term storage, such treated paper no longer shows abhesive characteristics.

In addition to the diificulties described above, particularly when using methylpolysiloxanes for anti-adhesion (abhesive) purposes, and even when using the more currently employed methyl hydrogen polysiloxanes for this purpose, it has been found that although release properties are improved, nevertheless, there is an undesirable tendency of the silicone in the abhesive paper to migrate to the surface of the paper thereby coming in contact with the material which it is desired to release. Often the abhesive paper is in contact with compositions which are destined to be used for adhesion applications, and the tack or the adhesion is undesirably reduced as a result of this migration of the orgauopolysiloxane from the treated release paper to the adhesive.

One particularly useful composition for the rendering of cellulosic materials non-adherent is the composition disclosed in my copending application Serial No. 723,965, filed March 26, 1958, now Patent No. 2,985,546, and assigned to the same assignee as the present invention. The composition of my aforementioned copending application comprises (1) a linear polydimethylsiloxane havinga terminal silicon bonded hydroxyl group, (2) a polyalkyl silicate, and (3) a tin salt selected from the class consisting of dibutyl tin dilaurate and dibutyl tin diacetate. While the composition of my aforementioned copending application has been found particularly useful, it has been found in commercial practice that the time required for the substantially complete curing of the composition is excessive in light of many commercial considerations. Thus, where commercial considerations require a cure in, for example, 60 seconds or less, at a temperature, for example, from about to 300 F., it is found that the cure under these conditions is not complete so that under these conditions the coating of the composition on cellulosic materials displayed excessive migration of silicone to the surface in which the coated cellulosic material was in contact and the incompletely cured coating showed poor abrasion resistance and could be easily'rubbed ofl of the coated cellulosic material.

Unexpectedly, I have discovered an improved composition for rendering cellulosic materials non-adherent which can be used to treat release paper whereby the vairous difficulties found in prior art coating compositions are obviated. In addition, release paper treated with these compositions shows no evidence of migration of the coating composition and the orgauopolysiloxane therein to the surface so as to contaminate any material with which the release paper may come in contact. Furthermore, the composition of my invention may be completely cured in times as low as 60 seconds at temperatures of from 180 to 300 F. to produce a release paper which is highly having anaverage of from 1.0'to 1.5 silicon-bonded methyl groups, an average of from 0.75 to 1.25 silicon-bonded hydrogen atoms,'and a total of from 2.0 to, 2.25 methyl and hydrogen groups attached to silicon and (3) a polyalkylsilicate, e,g., polyethyl silicate, etc, and (4) a tin salt selected from the class consisting of dibutyl tin di-' laurate and dibutyl tin diacetate. v r

The polydimethylsiloxanes employed in the practice of the present invention are those having the general formula r La l.-

where n isfaninteger greater than 1, for instance, from 25 to 100,000, Z is a member selected from the class consisting of, methyl and hydroxyl radicals, and R represents a member selected from the class consisting of hydrogen and trimethylsilyl groups. These polydimethylsiloxanes the .scope of Formula 1 include polydimethylsiloxanes which are chain-stopped at both ends of the chains. with tn'methylsilyl groups, polydimethylsiloxanes which are chain-stopped at one end of the chain with a trimethylsilyl'group and at the other end of the chain with a hydroxyl group, and polydimethylsiloxanes which are chain-stopped at both ends of the chain vvih hydroxyl groups. These polydimethylsiloxanes of the various types have the formulae, respectively, listed below:

The polydimethylsiloxanes of Formula 1 are soluble in organic solvents such as xylene, toluene, tiichloroethylene, etc., and are preferably of a fluid nature which may range in viscosity from highly fluid materials to difiicultly flowable-compositions. The viscositiesof such polydimethylsiloxanes may range from about 25 centipoises. to 10 millioncentipoises when measured at 25 C.

' These polydimethylsiloxanes are well known in the art and can be prepared by any one of several well known methods. The preparation of polydimethylsiloxanes which are chain-stopped at both ends of the chain are described in Patnode Patent 2,469,888.

High viscosity polydimethylsiloxanes which are chain terminated at both ends withtrimethylsilyl groups can be prepared by condensing the hydrolysis product of 'diinethyldichlorosilane with a minor amount of the hydrolysis product of trimethyldichlorosilane with either acid or alkaline catalysts such as hydrochloric acid, sulfuric acid, potassium hydroxide, etc. Alternatively, one can heat cyclic polymers of the formula sjz om where'm' is an integer equal to from 3 to 6, for example, octamethylcyclotetrasiloxane, with a minor amount of a 'trimethylsilylcontaining materi-alsuch as hexamethyldisiloxane to a temperature of from 125 to 175 for times ranging for about 15 minutes to two hours or more in the presence of an alkalinea'catalyst such as potassium hydroxide, cesium hydroxide, etc. In general, the alkaline catalyst is present in an amount equal, by weight, to about 0.001 to 0.1% based on the weight of the cyclic polymer of Formula 5. This procedure will result in a polydimethylsiloxane of Formula 1 having a viscosity of from about 500,000 to 10 million centipoises when measured at 25 C., depending on the amount of the trimethylsilyl-containing material used during the polymerization.

When the reaction mixture employed in the foregoing polymerization contains minor amounts of water, the resulting polydimethylsiloxane can contain molecules which are terminated at one or both ends with silicon-bonded hydroxyl groups. When lower viscosity polydimethylsiloxanes containing terminal silicon-bonded hydroxyl groups are desired, one can treat the high molecular weight products obtained above with water to reduce the viscosity of the polymer to within the range from about 25 to 100,000 centipoises at 25 C. This can be accomplished by blowing steam across the surface of the high molecular weight product or through the polymer for a sufficient time to give the lower viscosity material having the desired silanol content. Such compositions and various methods for preparing the same are more particularly described in U.S. Patent 2,607,792. The use of steam in this fashion will cause a decrease in the viscosity of the polymer while at the same time the formed linear polysiloxane will have terminal silicon-bonded hydroxy groups.

An alternative method for making thelinear organopolysiloxane containing terminal silicon-bonded hydroxy groups comprises adding water to the. high molecular Wei ght polymer described above in such amount that when heated at elevated temperatures, for instance, to C., the viscosity is reduced to the desired level of, for example, 1,000 to 50,000 centipoises- The amount of water used will vary depending upon such factors as the molecular weight of the polymer being treated, the time and temperature at which the mixture of high molecular weight organopolysiloxane. and water will be heated the ultimate viscosity desired, etc.

The amount of 'water used to reduce the molecular weight can be readily determined, For instance, one can obtain a linearfluid methylpolysiloxane'containing terminal silicon-bonded hydroxy groups and having a viscosity of from 1,000 to 2,000 centipoises at 25 C. by 'heating a high molecular weight methylpolysiloxane 1(prepared in accordance with the directions above) of about 2,000,000 centipoise viscosity with only 0.5%, by weight, thereof water for about 2 hours at 150 to 170 C. .The methyl hydrogen polysiloxanes employed in the practice or the present invention correspond to the formula where a has an average value of'from 1.0 to 1.5, b has an average value of from 0.75 to 1.25,"and the sum of a b is from 2.0 to' 2.25, inclusive. In general, these methylhydrogen polysiloxanes may be either linear or cyclic polysiloxanes. Thus, these methyl hydrogen polysiloxanes, if inlinear form may correspond to thegeneral formula r (7) ('JHa "I 7 (OH SiOSiOSi(GH Li l.

Generally, when there are dimethylsiloxy units in the methyl hydrogen polysiloxane, the molar concentration of such dimethylsiloxy units should not exceed more than 10 mol percent, and preferably is of the order of from to mole percent of the total number of siloxy units in the linear polysiloxane. Alternatively, the methyl hydrogen polysiloxane may be a cyclic methylpolysiloxane of the formula cn sino where q is a whole number equal to from 3 to or more. More particular directions for preparing the linear methyl hydrogen polysiloxane and the cyclic methyl hydrogen polysiloxane may be found in Wilcock Patent 2,491,843 and in Sauer Patents 2,595,890 and 2,595,891.

The polyalkyl silicate employed in the practice of the present invention can be obtained by effecting partial hydrolysis in water of monomeric organosilicates having the formula (YO) Si where Y is a lower alkyl radical containing from 1 to 5 carbon atoms, for instance, methyl, ethyl, propyl, butyl, amyl, etc., radicals. Such hydrolysis products are generally obtained by effecting partial hydrolysis in water of the particular monomeric organosilicate in the presence of small amounts of acid to a point where it is still water-insoluble and it is still possible to isolate a liquid, partially hydrolyzed organosilicon compound. Thus, taking as a specific example the controlled partial hydrolysis of ethyl silicate having the formula (C H O) Si, the hydrolysis of the latter may be carried out by adding acids or acid-forming metal salts to the liquid monomeric organosilicate, for instance, FeCl CuCI AlCl SnCl etc., and thereafter eifecting suitable hydrolysis of this mixture of ingredients in water to obtain the twophase composition from which the water-insoluble, partially hydrolyzed organosilicate can readily be separated from the aqueous phase and catalyst.

I have unexpectedly found'that contrary to what might be expected, dibutyl tin dilaurate and dibutyl tin diacetate gave minimum migration of the methylpolysiloxane and were able to be used in lower concentra tions than when one employed metallic soaps even tin soaps, such as tin octoate, tin naphthenate, tin oleate, and even such a metallic salt as butyl tin trioctcate, which is closely akin to dibutyl tin dilaurate and dibutyl tin diacetate.

The above essential ingredients used for treating cellulosic materials to render them adhesive in the form of a coating material which is non-migratory as far as the polydimethylsiloxane and the methyl hydrogen polysiloxane contained therein is concerned, are advantageously dissolved in a solvent such as, for instance, xylene, toluene, mineral spirits, trichloroethylene, perchloroethylene, etc. The above-described mixture of essential ingredients composed of the polydimethylsiloxane, the methyl hydrogen polysiloxane, the polyalkyl silicate, and the specific dibutyl tin salt in combination with a solvent can be used as treating baths for cellulosic materials such as cellulosic sheet material, parchment paper, kraft paper, linen rag paper, rice paper, glassine, cellophane, sulfite cellulose paper and the like; as well as sheeting or boxing materials such as paperboard, cardboard, pulpboard, and pasteboard.

A formulation comprising a solution of the above ingredients advantageously comprises, on a weight basis,

Although the dibutyl tin salt is employed on a weight basis as specified above, an alternative means for calculating the proportion of the dibutyl tin salt comprises basing iton the amount of tin contained therein; on such a basis one advantageously employs at least 0.1%, preferably from 0.5 to 25%, by weight, tin either in the form of the dibutyl tin dilaurate or dibutyl tin diacetate, based on the weight of the polydimethylsiloxane. The amount of dibutyl tin salt employed will depend upon such factors as, for instance, the particular metal salt used, its effect on the stability of emulsions, where emulsions are used; the type of organopolysiloxane employed, the type of paper to which the treating composition will be applied, the solubility of the tin salt, as well as the medium in which the tin salt will be used, the treating conditions including temperature and time of treatment, etc.

Following treatment of the cellulosic material with the solution of the above-described ingredients, the cellulosic material is advantageously dried by passing the treated material over heated rolls (or cans) maintained at temperatures of about to 350 F. for from 30 to seconds or more. The use of circulating hot air in this same temperature range and time is also satisfactory for efiecting cure of the treated cellulosic material. The particular time and temperature of cure employed in the practice of the present invention depends on a number of variables, such as the concentration of the dibutyl tin catalyst employed, the concentration of the methyl hydrogen polysiloxane, and the concentration and the par ticular type of polydimethylsiloxane employed in the coating composition. It has been found that with compositions witbin the scope of the present invention in which the polydimethylsiloxane is chain-stopped by silicon-bonded hydroxyl groups, such as the materials described in Formulae 3 and 4, the time required for curing is shorter than when a tn'methylsilyl chain-stopped polydimethylsiloxane of Formula 2 is employed in the composition. With the hydroxy chain-stopped materials of Formulae 3 and 4, very satisfactory cures in 60 seconds are obtained at temperatures of from 150 to 180 F. With the polydimethylsiloxane being trimethylsilyl chainstopped as in Formula 2, a satisfactory cure at 60 seconds is obtained with temperatures on the order of 250 to 350 F. During this curing or drying step, the optimum release properties of the treated paper are developed so that further heat treatment or aging is not required. These optimum release properties are immediately available upon completion of the heat curing step and at this time the release paper is abrasion resistant so that there is no tendency for the coating to wear ofi or break off.

As brought out above, the compositions of the present invention are curable at relatively low temperatures and in relatively short times. Accordingly, because of the highly curable nature of the compositions employed in the practice of the present invention, it is desirable to prepare the composition with the exception of the dibutyl tin dilaurate or diacetate catalyst and to add the catalyst shortly before the composition is to be used to treat cellulosic materials. The shelf life of the composition employed in the practice of the present invention varies with the particular organopolysiloxane and the catalyst concentration. In general the treating compositions have a room temperature shelf life of from 8 to 24 hours. Accordingly, it is possible to prepare a treating composition at the beginning of a days operation and use the catalyzed composition for the full days operation without danger of 5 gelation.

. controlled hydrolysis of tetraethyl silicate, the formula for said polyethyl silicate being described as follows:

i V SKOEQa E1; 0E1: o (EtO)3Si-0 iO%i0Si(OEt)a out in OEt where Et represents the C H group. [Additional information for making the partial hydrolysis products of the monomeric organosilicon compounds described above may be found in the article by H. D. Hogan and C. A. Setterstrom entitled Ethyl Silicates in Industrial and Engineering Chemistry, volume 39, page 1364, No. 11

In the examples which follow, two different polydimethylsiloxanes are employed. The first polydimethylsiloxane, which is referred to hereinafter as polydimethylsiloxane I, was a linear polydimethylsiloxane containing trirnethylsilyl groups at both ends of the siloxane chain. This material was obtained-by mixing octamethylcyclotetrasiloxane with about 0.001 percent, by weight, thereof of potassium hydroxide and 0.01 percent, by weight, thereof of decamethylpolysiloxane, with the reaction mixture containing less than five parts per million of water. This reaction mixture was heated for about 4 hours at 145 C. until a benzenesoluble fluid was formed which had a viscosity; of about 2 million centipoises when measured at 25 C. 1

The second polydimethylsiloxane employed in the examples, hereinafter referred to as polydimethylsiloxane II, was. a 'polydimethylsiloxane in.which both ends of the siloxane chain were terminated with silicon-bonded hydroxyl groups. This material was prepared by mixing octamethylcyclotetrasiloxane with 0.001 percent, by Weight, of potassium hydroxide and 0.1 percent, by weight, of water and heating the. resulting mixture for about 4 hours'at 150 C. until abenzene soluble product having a viscosity of about 1 million centipoises at 25 C. was

obtained.

The methyl hydrogen polysiloxane used in the following'examples was a linear tn'methyl silyl chain-stopped polysiloxane described in Wilcock Patent 2,491,843, and had a viscosityiof 100 centipoises when measured at 25 'C. This material-was obtained by cohydrolyzing 5. parts (CH 'SiCl and 95 parts CH SiHCl In the following-tests, the release characteristics of the treated paper (parchment paper was used) were determined by pressing (by hand) a strip of surgical adhesive tape on the surface of the treated paper and lifting the tape from the paper; evaluation of the release Was determined by assigning numerical values as follows:

O-No lifting of paper whatever .1One edge of paper lifted up to A" 2One edge of paper lifted A to 1 3One edge of paper lifted 1" to 2" 4Paper falls off after being lifted by tape 5-'Paper shakes off after being lifted by tape 6--Paper will not shake off Migration of the silicone from the treated paper to the surface with which it came in contact was determined by observing the detackification of a surgical adhesive tape (loss of tack of the adhesive) caused by migration of the silicone from the surface of the paper to the adhesive on the tape. This was accomplished by pressing (by hand) a strip of adhesive tape onto the surface of the treated paper five times in five difierent areas. This technique greatly accelerated determination of migration because the adhesive would beexpected to pull off silicone which, if given sufficient time, might migrate of its own accord to the material with Whichit came in contact. Surgical adhesive tape was used because a major. application of release paper in its use as interleaving sheets where thetreated paper is in intimate contact with adhesives and no loss of tack can be tolerated in such an application. A strip of the adhesive tape was then lifted fromthe paper and folded over so that the adhesive surface (which had been in contact with the release paper) was brought into contact with itself. The pull required to separate the adhesive surface from itself (evaluated subjectively as to poor, fair, fair-good, and good tack) compared with tape which had not been in contact with release paper, was used as a measure of detackification of the tape and thus as a measure of migration of the silicone material. The silicone pickup was within the range from about 0.1% to 2%, by weight, based on the weight of the parchment paper which was treated in every instance in the following'examples.

The abrasion resistance or rub 01f of the coated cellulosic material was determined by rubbing a thumb across the surface of coated paper and observing whether the coating material rubs oii or peels olf. If the coating material rubs off or peels off the coated paper is rated poor. If there is no rub off of the coating material from the coated paper, the rub ofi is rated good.

In the following examples, the material treated with the various treating baths was parchment paper which was treated by immersing the paper in the bath, removing the treated paper and passing it between squeeze rolls. Thereafter the treated paper was given the heat treatment specified and immediately thereafter the release, the migration or detack, and the rub ofi were determined.

' Example 1 In this example a solution was prepared composed of 9.26 parts of polydimethylsiloxane I, 0.935 part of the ethyl silicate, 0.1 part tin added as a solution of 50 parts of dibutyl tin dilaurate in parts of xylene, and 89.3 parts of toluene as a solvent. This solution is known as Solution A. Solution B was prepared-by mixing 909 parts of polydimethylsiloxane I, 0.935 part of the ethyl silicate, 0.1 part of tin added as a solution of 50 parts of dibutyl tin dilaurate in 100'parts xylene, 0.17 part of the methyl hydrogen polysiloxane fluid described above, and 89.7 parts of toluene as a solvent. Both solution A and solution B were applied'to parchment paper by the method previously described and thereafter heated for 60 seconds at 300 F. The release of both of the treated papers was 0 immediately after curing. The detack of solution A was only fairimmediately after curing while that of solution B was good. The rub off of solution A was poor immediately after. curing while the rub oif of solution Bzwas good after curing. Thus, this example establishes that both the detack and the rub ofi of cellulosic materials treated by the process of the present invention are far. superior to these properties in papers treated by similar materials which do not, however, contain a methyl hydrogen polysiloxane.

Example 2 In this example, a solution was formed from 9.26 parts of polydimethylsiloxane 11, 0.935 part of the ethyl silicate, 0.1 percent tin added as a solution of 50 parts dibutyl tin dilaurate in 100 parts of xylene, and 89.7 parts of toluene and was identified as solution C. Solution D was prepared from 9.09 parts of polydimethylsiloxane H, 0.935 part of the ethyl silicate, 0.1 part tin added in the same manner as in solution C and 0.17 part of the methyl hydrogen polysiloxane described previously. Both of these solutions were applied to parchment paper by methods previously described and were heat-treated for 60 seconds at 180 F. At this time the release of both treated papers was 0. However, the detack for solution C was only fair while the detack for solution D was good. Similarly, the rub 01? for the paper treated with solution C was poor while the rub oif for the paper treated with solution D was good. Thus, this example provides further evidence of the unexpected superiority of the compositions of the present invention over compositions a v '9 which differ therefrom by virtue of the. absence of the methyl hydrogen polysiloxane.

Example 3 This example is illustrative of the use of more concentrated solutions of compositions within the scope of the present invention and the comparison of these compositions with prior art compositions. Specifically, a solution was prepared (Solution E) of 27.25 parts of polydimethylsiloxane I, 2.75 parts of the ethyl silicate, 0.3 part tin added as a 33 percent solution of dibutyl tin dilaurate in xylene, and 70 parts toluene. Another solution was prepared (Solution F) from 26.75 parts of polydimethylsiloxane I, 2.75 parts ethyl silicate, 0.3 part tin added as in solution E, 0.50 part of the aforementioned methyl hydrogen polysiloxane, and 70 parts toluene. When the properties of these two solutions were measured immediately after application of the solutions to parchment paper and curing for 60 seconds at 300 F., it was found that the release of both papers was 0, the detack of solution E was poor as compared with the good detack of solution F, and the rub olf of solution E was poor as compared with the good rub off of solution F.

Example 4 This example serves as a further illustration of the use of more concentrated solutions of the compositions of the present invention and of the comparison of these compositions with prior art materials. Specifically, solution G was prepared of the same proportions of ingredients as in solution E of Example 3, except that polydimethylsiloxane II was substituted for polydimethylsiloxane I. Solution H was prepared of the same proportions of ingredients asin solution F of Example 3, except that polydimethylsiloxane II was substituted for polydimethylsiloxane 1. After application of solutions G and H to parchment paper and heat-treating the coated parchment papers for 60 seconds at 180 F., it was again found that the release of both papers was 0. However, the detack of the paper treated with solution G was poor while that treated with solution H was good. The rub ofi of the parchment paper treated with solution G was poor while the rub ofi of the paper treated with solution H was good.

Example 5 A solution is formed by mixing two parts of polydimethylsiloxane I with 10 parts of a methyl hydrogen polysiloxane having a viscosity of 200 centistokes at 25 C., 0.1 part of the polyalkyl silicate, 0.01 part of dibutyl tin diacetate added as a 50% solution in xylene, and about 88 parts by weight of mineral spirits. Upon application of this solution to parchment paper with subsequent cure for 60 seconds at 350 C., the resultant paper has release, good detack, and good rub off.

Example 6 A solution is prepared by mixing 1 part of a linear chain-stopped polydimethylsiloxane having both ends of the chain terminated with silicon-bonded hydroxyl groups and having a viscosity of 1,500 centipoises at 25 C., 0.01 part of the methyl hydrogen polysiloxane employed in Example 5, 2 parts of the polyalkyl silicate, parts of dibutyl tin diacetate added as a 33 percent solution in xylene, and about 92 parts of xylene. When this solution is applied to paper and cured for 90 seconds at 150 F., the resulting paper has 0 release, and good detack and rub ofi.

It will, of course, be apparent to those skilled in the art that in addition to the particular polydimethylsiloxanes illustrated in the examples, and the particular methyl hydrogen polysiloxanes illustrated in the examples, other organosilicon materials can be employed without departing from the scope of the present invention. The concentration of the polydimethylsiloxane, as well as of the catalyst and the methyl hydrogen polysiloxane may be varied within the ranges previously recited, again within the scope of the present invention. Furthermore, instead of employing a single polydimethylsiloxane in the composition, it is also possible to employ mixtures of various polydimethylsiloxanes such as polydimethylsiloxanes falling within the scope of Formulae 2, 3, and 4. The concentration of the dibutyl tin dilaurate or the dibutyl tin diacetate, or mixtures of such tin salts, may also be varied within wide limits depending on the factors recited previously.

The amount of silicone which is picked up by the cellulosic material as a result of the treatment with the solution of the present invention depends upon such factors as the absorbency of the cellulosic material, the method of application, the concentration of the solution, etc. Generally, the amount of pickup ranges from about 0.1 to about 5% or more, based on the dry weight of the cellulosic material; the preferred pickup being within the range or" about 0.5 to about 2% silicone pickup. Obviously, larger amounts of silicone pickup may be employed, but generally this is not necessary and usually serves merely to increase the cost of the treatment. The ability to obtain maximum pickup with minimum amounts of silicone and to realize the maximum release properties is one of the unexpected and unobvious advantages of employing the particular combination of ingredients herein described for release purposes.

Advantages of using the compositions herein described for the above specified purposes are manifold. By means of my invention, it is possible to obtain high quality release characteristics for highly adherent materials such as uncured synthetic rubbers, pitch, asphalt, tar, many adhesives and other type of materials. The anti-blocking properties are effective even at low concentrations of silicone pickup; the paper treated can be heated at low temperatures of from to 350 F., which is usually sutficient to bring out the optimum properties of the re lease paper Without the necessity of employing abnormally high temperatures which are often impractical to use in paper making establishments.

Of equal significance is the fact that paper treated in accordance with my process can be employed at once for its anti-release purposes with realization of essentially optimum properties. Heretofore, organopolysiloxanes previously available on the market for the same purpose required aging, that is, storing of the treated paper for times as long as six weeks, in order to bring out the optimum release characteristics of the treated paper. Of considerable importance is the fact that even at high temperatures, the release characteristics are maintained at optimum levels and elevated temperatures do not destroy the release film. The compositions for treating cellulosic materials herein described are readily amenable to a single step procedure and are easily regulated and controlled for adjustable silicone pickup by minor variations in formulations. Standard paper making or paper converting equipment is readily employed in connection with the treating operations and no precautions need be taken for any toxic materials which may be contained in the treating solutions.

Cellulosic materials treated as described above have a wide range of usefulness. Thus, asphalt or high molecular weight organic polymers, such as various synthetic rubbers, can be poured hot into containers fashioned from the treated paper or paperboard, and after cooling it will be found that solidified asphalt or polymer is readily and cleanly separated from container walls.

My invention permits paper treated in accordance with my process to be substituted for various fabrics which have heretofore been used in contact with adhesive surfaces of electricians pressure-sensitive tape, adhesive tapes used for surgical purposes, and regenerated cellulose tapes carrying a permanent adhesive upon one surface. Vulcanized or unvulcanized sheets of rubber can be prevented from adhering to each other despite the fact that these sheets of rubber are quite sticky and cohesive when in a oesne completing the baking cycle in the original container in V which the baked goods are purchased.

' What I claim asnew and desire to secure by Letters Patent of the United States is: V

1. The method of rendering cellulosic fibrous sheet material non-adherent to surfaces which normally adhere thereto, which comprises treating said material with a treating bath containing as sole active ingredients (1) a linear polydimethylsiloxane in which the siloxane chain is terminated bya memberselected from the class consisting of silicon-bonded hydroxyl groups and siliconbonded trimethylsiloxy groups, (2) a methyl hydrogen polysiloxane, (3) a polyalkyl silicate, and (4) a metallic salt selected from the class consisting of dibutyl tin dilaurate and dibutyl tin diacetate. V

.2; Cellulosic sheet material treated in accordance with the method described in' claim 1.

3 The method for rendering cellulosic fibrous sheet material non-adherent to surfaces which normally adhere thereto, which process comprises treating the cellulosic fibrous sheet material with a treating bath consisting essen-' tially of, by weight, the following active ingredients: (1) from 1 to 30 parts of a linear polydimethylsiloxane in which the siloxane chain'is terminated by a member selected from the class consisting of silicon-bonded hydroxyl groups and silicon-bonded trimethylsiloxy groups, (2) from 0.01 to parts of a methyl hydrogen polysiloxane, (3) from 0.01 to 40 parts'of a polyalkyl-silicate, (4) from 0.01 to' 0.5 part of a metallic salt selected from the class consisting of dibutyl tin dilaurate and dibutyl tin diacetate and (5) from 60 to 97 parts of an organic solvent,

5. The method of-claim 4. in which thelinear polydi-e methylsiloxane is terminated by silicon-bonded hydroxy groups. 7 g 7 6. The method for rendering cellulosic fibrous sheet material non-adherent to surfaces which normally adhere thereto, which process comprises treating the cellulosic fibrous sheet material with the treating bath consisting essentially of, by weight, the following active ingredients: (1) from 1 to 30 parts of a linear polydimethylsiloxane containingterminal silicon-bonded hydroxy groups, (2) from 0.01 to 10 parts of a methyl hydrogen polysiloxane, (3) from 0.1 to 40 parts of apolyethyl silicate, (4) from 0.01 to 5 partsdibutyl tin dilaurate, and (5) from to 97 parts of an organic solvent,

7; The method for rendering cellulosic fibrous sheet material non-adherent to surfaces which'normally adhere thereto, which process comprises treating the cellulosic fibrous sheet material with a treating bath consisting essentially of, by weight, the following active ingredients: (1) from 1 to 30 parts-of a linear polydimethylsiloxane containing terminal silicon-bonded hydroxy groups, '(2) from 0.01 to 10 parts of a methyl hydrogen 'polysiloxane, (3) from 0.1 to 40 parts of polyethyl silicate, .(4)' from 0.01 to 5 parts of dibutyl tin diacetate and (5) from 60 to 97 parts of an organic solvent.

References Cited in the file of this patent UNITED STATES PATENTS 2,504,388 Braley Apr. 18, 1950 2,588,367 Dennett Mar. 11, 1952 2,814,601 Currie et a1 Nov. 26, 1957 2,843,555 Berfidge July 15, 1958 2,884,074 Lewis et al. May 5, 1959 2,895,853 Bailey et al. July 21, 1959 FOREIGN PATENTS 804,198 Great Britain "Nov. 12,1958 

1. THE METHOD OF RENDERING CELLULOSIC FIBROUS SHEET MATERIAL NON-ADHERENT TO SURFACES WHICH NORMALLY ADHERE THERETO, WHICH COMPRISES TREATING SAID MATERIAL WITH A TREATING BATH CONTAINING AS SOLE ACTIVE INGREDIENTS (1) A LINEAR POLYDIMETHYLSILOXANE IN WHICH THE SILOXANE CHAIN IS TERMINATED BY A MEMBER SELECTED FROM THE CLASS CONSISTING OF SILICON-BONDED HYDROXYL GROUPS AND SILICONBONDED TRIMETHYLSILOXY GROUPS, (2) A METHYL HYDROGEN POLYSILOXANE, (3) A POLYALKYL SILICATE, AND (4) A METALLIC SALT SELECTED FROM THE CLASS CONSISTING OF DIBUTYL TIN DILAURATE AND DIBUTYL TIN DIACETATE. 